swift234

Don't add capture arguments to default argument generators.

If we ever add the ability for default arguments to refer to
enclosing variables, we should promote DefaultArgumentInitializer
to be an always-present entity, give it an independent capture
list, and make SILDeclRef refer to it directly.  In fact, we may
want to do that anyway.  Until then, it's a weird special case
in terms of not really being a reference to the function returned
by getAnyFunctionRef().

rdar://24242783